1. Field of the Invention
The present invention relates to construction machines such as hydraulic excavators provided with cabins.
2. Description of the Related Art
A cabin frame 12 constituting a cabin 4 shown in FIG. 6 is composed of front pillars 13 and 14 disposed on the left and right, respectively, rear pillars 15 and 16 disposed on the left and right, respectively, a center pillar 17 disposed on the left and between the front pillar 13 and the rear pillar 15, a left roof member 18 disposed on the left and spanning the upper ends of the front pillar 13 and the rear pillar 15, a right roof member 19 disposed on the right and spanning the upper ends of the front pillar 14 and the rear pillar 16, an upper front cross member 20 spanning the upper ends of the left front pillar 13 and the right front pillar 14, and an upper rear cross member 21 spanning the upper ends of the left rear pillar 15 and the right rear pillar 16.
The cabin frame 12 may receive loads which are generally classified as a load F1 received from the left in machine rollover (turnover) or the like (hereinafter, referred to as a lateral load), a load F2 received from the rear (similarly, referred to as a rear load), and a load F3 received vertically from the upper portion to the lower portion (similarly, referred to as a vertical load).
Accordingly, in view of ensuring safety for the operator, it is required to ensure the existence of a space for the operator, particularly, a rear space where the operator is located, even if the cabin frame 12 is deformed due to these loads.
To meet this requirement, the cabin frame 12 employs a configuration including a front gate structure composed of the front pillars 13 and 14 and the upper front cross member 20, and a rear gate structure composed of the rear pillars 15 and 16 and the upper rear cross member 21, the front and rear gate structures being connected to each other with the roof members 18 and 19.
In addition, there have been suggested as a method of reinforcing the cabin frame 12, various configurations such as a configuration in which wide pillars extending from the intermediate portions in the front-back direction of both the left and right sides toward the upper rear are added (refer to Japanese Unexamined Patent Application Publication No. 2002-327462), and a configuration in which front and rear gate structures are connected to each other with a platy roof member (refer to Japanese Unexamined Patent Application Publication No. 2001-123482).
The cabin frame 12 that supports the loads only with the gate structures may not sufficiently provide a supporting capability against the lateral, rear and vertical loads F1, F2, and F3.
Meanwhile, when the reinforcement is added to the configuration in addition to the gate structures, the reinforced structure may have to be large in order to obtain a high reinforcing effect, resulting in problems such as a considerable increase in the weight of the cabin frame, or a degradation in the field of view of the cabin.
However, a technique in which a relatively small-scale reinforcement is added, for instance, merely connecting the left and right rear pillars 15 and 16 with a beam, may not provide a sufficient reinforcing effect.